1. Field of the Invention
The present invention relates to an endless belt conveying apparatus having an endless belt and to a toner image heating apparatus having the endless belt conveying apparatus. The endless belt conveying apparatus and the toner image heating apparatus are used to an image forming device of an electrophotographic copy machine, facsimile, and printer or to a composite machine and the like having a plurality of functions of them.
2. Description of the Related Art
There are known fixing apparatuses of a system for permanently fixing an unfixed toner image by pressing and heating it by causing a recording material, which bears the unfixed toner image on the upper surface thereof, to come into intimate contact with an endless-belt-like fixing film and to pass the unfixed toner image together with the fixing film through a fixing nip portion between a pressure rollers and the fixing film. The endless-belt-like fixing film is trained around a drive roller and a driven roller and travels in rotation, and when the fixing film moves while offsetting to one side in a width (belt width) direction during the travel, it continuously offsets until it comes into contact with other member.
A structure as shown in FIG. 19 is ordinarily known to as a structure for preventing offset. In this case, flanges 112 are standingly disposed on both the ends of a roller in the width direction thereof, and when a belt 104 is offset, an edge thereof is caused to come into contact with the flange 112 so that the belt 104 is prevented from being further offset. However, the ordinary structure is disadvantageous in that the edges of the belt 104 and the flanges 112 on the roller side are in sliding contact with each other and worn.
Incidentally, as shown in FIG. 20, it is considered that the belt is offset mainly by that the rotational axis lines of both the drive roller 102 and the driven roller 103 are not in parallel with each other and thus relatively inclined. Accordingly, the offset of the belt can be suppressed by correcting the inclination of the rollers. The applicant previously proposed a fixing apparatus provided with a structure for preventing an offset of a belt (refer to, for example, Japanese Patent Application Laid-Open No. 2-157880). The structure will be briefly described referring to FIG. 20.
Offset detection sensors 113a, 113b are disposed on both the edge sides of a belt 104 in the width direction thereof, and the offset of the belt is suppressed by correcting the inclination of the rotational axis line of the driven roller 103 by an adjustment mechanism. That is, when the belt 104 is offset in the direction of an arrow B in the belt width direction while it travels in rotation in the direction of an arrow A, the offset detection sensor 113b detects the offset. The rotational axis line of the driven roller 103 is lowered on the proximal side thereof in FIG. 21 which is opposite to the direction of the arrow B by operating the adjustment mechanism in the direction of an arrow C based on a result of detection. When the inclination of the rotational axis line of the roller, that is, a “roller axial angle” is corrected as described above, the belt 104 moves back in the direction of an arrow D, thereby the belt 104 can be corrected to a normal attitude. When the belt is offset in a direction opposite to the direction of the arrow B, the offset detection sensor 113a detects the offset and lifts up the driven roller 103 on the proximal side thereof in the direction of an arrow E as shown in FIG. 22, With this operation, the belt 104 moves back in an F direction and is corrected to the normal attitude.
While the belt travels in rotation, the inclined roller rotational axis line, that is, a roller axial angle is alternately corrected repeatedly. That is, when the belt 104 is offset to one side in the belt width direction, the one side is lifted up, whereas when it is offset to the other side, the other side is lifted up, thereby the belt 104 is caused to continuously travel in rotation while alternately repeating the correction.
However, components and equipments such as a motor acting as a power source, a speed reduction gear train, an offset detection sensor, and the like for adjusting the roller axial angle of the driven roller 103 are necessary in the offset prevention mechanism disclosed in Japanese Patent Application Laid-Open No. 2-157880. Accordingly, there is a possibility that the size and cost thereof are increased and thus there is a room for improving the offset prevention mechanism.